1. Technical Field of the Invention
The present invention relates to the technical field of an image processing method and an image processing apparatus which perform a correction of image quality deterioration such as chromatic aberration of magnification, distortion aberration, deterioration of marginal luminosity, defocusing or the like derived from a taking lens that occurs in an image recorded with a film with lens, a low-priced compact camera, a digital camera or the like in a digital photoprinter or the like which obtains image data either by photoelectrically reading an image optically recorded with a taking lens of a silver halide type photographic camera or the like or direct from an image recorded with the digital camera or the like and then subjects the thus obtained image data to predetermined processing to obtain a print (photographed) reproducing the recorded image as an output image.
2. Prior Art
Heretofore, the images recorded on photographic films such as negative films and reversal films (which are hereunder referred to simply as "films") have been commonly printed on light-sensitive materials (photographic paper) by means of areal exposure, namely, direct (analog) exposure in which the light-sensitive materials are exposed by projecting the image on the film.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, the image recorded on a film is read photoelectrically, converted to digital signals and subjected to various image processing operations to produce image data for recording purposes; recording light that has been modulated in accordance with the image data is used to scan and expose a light-sensitive material to record an image (latent image), which is subsequently developed to produce a print (photograph). The printer operating on its principle has been commercialized as a digital photoprinter.
In the digital photoprinter, images are handled as digital image data so that an image processing condition at the time of printing can be established by image data processing. Therefore, correction of washed-out highlights or dull shadows caused by photographing with backlight, an electronic flash or the like, sharpness processing (sometimes referred to simply as "sharpening") or the like are favorably performed to produce a high quality print which has never been realized by a conventional direct exposure.
However, a case may occur that even if image data processing is performed on the image data of the image taken or recorded on the film, quality of the output image on the print can not adequately be improved. The case, for example, illustrates chromatic aberration of magnification, distortion aberration, deterioration of marginal luminosity, defocusing or the like derived from performance (aberration characteristic) of a lens mounted on the camera used to take the image.
A color image is formed of three primary colors: red (R), green (G) and blue (B). Since refractive index of the lens (imaging magnification) varies subtly with wavelength, the imaging magnifications of R, G and B lights are different from each other to generate the chromatic aberration of magnification. As a result, the image reproduced from the film has a definite color divergence.
In order to obtain a satisfactory and appropriately recorded image, a plane that is perpendicular to an optical axis must be focused on an imaging plane in correspondence with the plane. In fact, however, an ordinary lens has the imaging positions displaced along the optical axis and the resulting displacements of the focused positions in the axial direction cause the distortion, namely, distortion aberration of the focused image. As a natural consequence, the reproduction of the image taken on the film is distorted.
Moreover, in the image focused through the taking lens, by originating in a lens (aberration) characteristic that luminosity is deteriorated from the center area toward marginal areas of the image in accordance with so-called law of cosine to the fourth power (cos.sup.4), luminosity at the marginal areas or edges of the image becomes insufficient or dark, namely, so-called deterioration of marginal luminosity occurs.
Also, owing the aberration characteristic of the taking lens, a focal divergence increases in the marginal areas of the image to generate defocusing (Point Spread Function: PSF) therein.
In such way, owing the aberration characteristic of the taking lens, image quality deterioration such as color divergence, distortion in shape, deterioration of marginal luminosity, defocusing or the like occurs in the output image.
If a camera such as a single-lens reflex camera or the like that needs a cost to some extent is used, high-precision lens elements may be used and a plurality of lens elements combined to correct various aberrations including chromatic aberration of magnification, distortion aberration, deterioration of marginal luminosity, defocusing and the like may be used whereupon an appropriate image can be recorded on the film. However, cameras such as films with lens and compact cameras required to be a low cost can not use high-cost lenses so that the image quality deterioration such as chromatic aberration of magnification, distortion aberration, deterioration of marginal luminosity, defocusing or the like will develop in the images recorded on films. As a result, the image reproduced on the print will eventually be of low quality.
To deal with this problem of image quality deterioration which can not enhance the image quality of output image on the print, techniques have been proposed in connection with an image processing method and apparatus and typical examples of such technologies are disclosed in Unexamined Published Japanese Patent Applications (kokai) No. 287360/1995 and No. 281613/1997. The latter discloses the technique related with an image processing method and apparatus which perform image corrections in accordance with the aberration characteristic of a lens obtained via a lens information acquisition device. It points out that the technique can correct the aberration derived from the lens, prevent the image quality deterioration at marginal areas of the image and obtain a high-quality image in a constant manner.
The former example, i.e., Unexamined Published Japanese Patent Application (kokai) No. 287360/1995, points out that processing information of a film with lens, for example, a lens type recognizing code (code number for recognizing the type of the taking lens) of the taking lens of the film with lens is recorded on the film or the like of the film with lens; then the thus recorded lens type recognizing code is automatically read by utilizing a reading device or the like; hence the deformation caused by the distortion which has been derived from the aberration characteristic of the taking lens can be corrected.
However, a case may occur that the lens type recognizing code of the taking lens can not be obtained because the lens information acquisition device made a reading error of the lens type recognizing code of the taking lens, or because the lens type recognizing code itself of the taking lens has not been recorded. In this case, the aforementioned ordinary technique is not capable of correcting image quality deterioration (hereinafter referred to simply as "image correction") in some cases derived from the taking lens such as distortion aberration, chromatic aberration of magnification, deterioration of marginal luminosity, defocusing or the like so that it can not prevent the image quality deterioration. Moreover, there are some cases in which information related with the lens is obtained; correction intensity to perform the above-mentioned image correction is automatically selected based on the thus obtained information; and the correction of image quality deterioration is performed, when the film is a film with lens which is exposed in a curved form, the correction of aberration can not be appropriately performed only by correcting the aberration characteristic of the taking lens so that distortion aberration or chromatic aberration of magnification still remains uncorrected on the image after subjected to correction; hence, the image quality deterioration can not be prevented.
In a conventional way, the reproduced image after subjected to image correction can not be verified on a monitor so that an operator is not always capable of obtaining a satisfactory print and must print out the reproduced image after subjected to correction to judge whether the image is appropriate or not. Moreover, the operator conventionally establishes correction intensity such as correction direction, correction quantity and the like on each of the images recorded on the film judging from the film to perform the correction of image quality deterioration on an image basis so that the operator must print out the reproduced image after subjected to correction from image to image to judge whether the correction is appropriately performed or not. Hence, there is a problem of aggravation of efficiency due to a significant waste of time and print output.
Further, when the image correction is performed on all of the images recorded on the film, if information on the taking lens can not be obtained so that image correction can not be automatically performed based on the aberration characteristic of the lens, though the lens used in shooting being the same and therefore the lens aberration is the same, a correction condition must be manually set from frame to frame; hence, there is a problem that appropriate and uniform images can not be obtained in a rapid and effective way by the same image correction which does not depend on individual frames.
There is a case in which all images recorded on the film were not always taken with the same camera, namely, a lens having the same aberration characteristic; there is also another case in which images recorded on the same film have different image quality deterioration such as distortion aberration, chromatic aberration of magnification, deterioration of marginal luminosity, defocusing or the like from each other. In these cases, there is a problem that the same image correction can not be performed on all images recorded on one film.
In the case of the film, particularly, of an ordinary 135 size or a film with lens, the above-mentioned correction of image quality deterioration can not be performed by the above-mentioned technique which automatically performs correction by reading the recognizing code of the film with lens involving lens type, for example, the lens type so as to automatically recognize the lens type. Hence, there is a problem that the image quality deterioration can not be prevented.
In such case, for the purpose of correcting the image quality deterioration such as distortion aberration, chromatic aberration of magnification, deterioration of marginal luminosity, defocusing or the like, it may be possible that firstly an image correction method of each image, correction intensity or the like based on its correction image correction method is manually designated, secondly whether the correction is appropriate or not is judged as looking at the corrected image displayed on a monitor and lastly an appropriate correction is established. However, an establishing operation of the appropriate correction of each image as looking at the monitor on an image basis is troublesome for the operator and aggravates work efficiency when a voluminous printout is performed. Moreover, a case may occur that correction of aberration derived from the taking lens is overlooked; hence, there is a problem that a high-quality image can not always be obtained.